Toolless method for alignment, retention, connection, termination and test on printed circuit boards

ABSTRACT

Embodiments of the present invention provide a system for testing and mounting a PCB in a device. A PCB may be placed on one or more standoffs so that a head portion of the standoff protrudes from one or more apertures of the PCB. A push-pin type standoff cap may then be placed on the protruding heads to mechanically restrain the PCB to the standoffs. Furthermore, one or more cables may be coupled with the standoff caps to provide power or test signals to one or more connector pads on the PCB. Therefore, the standoff caps provide a system for aligning, retaining, connecting, terminating, and testing printed circuit boards.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 11/458,743 filed Jul. 20, 2006, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally relates to a system for mounting andtesting printed circuit boards, and more specifically a system foraligning, retaining, connecting, terminating, and testing printedcircuit boards.

2. Description of the Related Art

Most electronic devices today contain one or more Printed Circuit Boards(PCB). A PCB is used to mechanically support and electrically connectcomponents of a device using conductive pathways called traces. Forexample, a computer usually contains a PCB called the motherboard. Themotherboard contains the essential components of the computer such asthe microprocessor and main memory, along with other basic components.The components may be housed in sockets and connected to each otherusing the traces.

During assembly of electronic devices, one or more PCBs may be securedto each other or to a device frame or chassis. Securing the PCBs usuallyinvolves fastening the PCB to another PCB, or to the device chassis,using screws. The PCB is usually secured on one or more standoffs.Placing the PCB on a standoff ensures airflow along both surfaces of thePCB, thereby allowing cooling during operation of the device. Thestandoffs also prevent undesired contact between active circuits of thePCB and other device components.

FIG. 1 illustrates the mounting of a PCB 110 on a chassis 120. Chassis120 may contain one or more standoffs 121 on which the PCB may bemounted. As illustrated, standoffs 121 may be hollow cylindricalsleeves, the inner portion of the sleeve providing threading forfastening screws. During installation, the PCB is placed on thestandoffs so that one or more apertures 112 of the PCB align with theone or more standoffs 121. A screw 111 may then be passed through eachof the apertures 112 and secured to the standoffs 121 by means of thethreaded inner sleeves of the standoffs.

One problem with the prior art is that the PCB installation can be quitelaborious and time consuming. The PCB must first be aligned with thescrew holes. The screws must then be tightened while keeping the PCBaligned with the screws. Maintaining alignment makes assembly slow andinefficient.

Screw installation requires additional tools and application of force totighten the screws which may increase the risk of damage to sensitivecomponents of the PCB. Furthermore, the screws are usually small and maybe dropped on the PCB and other components or lost in the device,thereby increasing the risk of damage even further. Because screws aremade of conductive materials, there is also a danger that the screws, ifdropped in the device, may create undesired short circuits.

PCBs are also routinely subject to diagnostic testing prior toinstallation in a device. For example, the diagnostic testing mayinclude connectivity testing to determine operating characteristicsbased on response of the PCB to imposed test signals. One or moreconnectors are typically attached to the PCB to facilitate testing. Theconnectors serve to connect one or more test cables that impose testsignals on the PCB under test. For example, a connector 113 is shown inFIG. 1. FIG. 2 illustrates an enlarged bottom view of a PCB with aconnector 113 and a standoff 121.

One problem with using prior art connectors is that testing can be timeconsuming and tedious. Typically, connectors serve to connect a singlecoaxial test cable to the PCB in order to perform a single testingfunction. Thus, when performing multiple tests, testing cables must beuncoupled from original connectors and re-coupled to other connectors.Alternatively, users may couple different testing cables to the sameconnector to perform other tests. However, this requires on-board logicto multiplex signals. The use of connectors and/or multiplexing logicmay take up valuable space on the PCB. One skilled in the art willrecognize that real estate on PCBs is precious given the increasingdemand for greater functionality from smaller devices.

Yet another problem, as illustrated in FIG. 2, is that connectors aretypically unsupported when mounted. Thus, the use of force when couplingcables to the connectors could crack or otherwise damage the PCB.Furthermore prior art connectors remain on the PCB after testing andeven after the device is commercialized. Leaving connectors on the PCBcan be very costly, especially given that some connectors may even begold plated.

Therefore, what is needed is are improved methods, systems, andapparatus for efficient and safe installation and testing of PCBs.

SUMMARY OF THE INVENTION

The present invention generally relates to a system for mounting andtesting printed circuit boards, and more specifically a system foraligning, retaining, connecting, terminating, and testing printedcircuit boards.

One embodiment of the invention provides a mounting device for mountinga printed circuit board (PCB). The mounting device generally comprises astandoff comprising a body and a securing element disposed in andprotuding from the body, wherein the body forms a PCB resting surface atan interface of the securing element and the body and wherein thesecuring element is configured to be registered with and disposedthrough an aperature formed in the PCB. The mounting device furthercomprises a standoff cap comprising a hollow sleeve configured toaxially receive the securing element and mechanically restrain the PCBagainst the PCB resting surface of the standoff, wherein an innersurface of the hollow sleeve and an outer surface of the securingelement define a locking interface to resist relative axial movement.

Another embodiment of the invention provides a method for testing a PCB.The method generally comprises placing the PCB on a plurality ofstandoffs, each standoff comprising a body, a securing element disposedin and protruding from the body, and a PCB resting surface formed at aninterface of the head and the body, wherein the securing element isnarrower than the body thereby allowing each securing element toregister with and be disposed through an aperture formed in the PCB andallowing the PCB to rest on the respective PCB resting surface. Themethod further comprises securing the PCB to the standoffs by fitting astandoff cap over a portion of each securing element protruding from theapertures, wherein one or more of the standoff caps include one or moreelectrically conductive elements coupled to one or more respectiveelectric cables for carrying test signals, and registering the one ormore conductive elements with one or more connector pads on the PCBsurface to exchange test sigals with the PCB.

Yet another embodiment of the invention provides a device, generallycomprising a plurality of standoffs connected to one of a device chassisand a device component, the standoffs each comprising a body and asecuring element disposed in and protuding from the body, wherein thebody forms a PCB resting surface at an interface of the securing elementand the body, a PCB disposed on the respective PCB resting surface ofthe standoffs and wherein the PCB defines a plurality of apertures eachhaving a respective one of the securing elements of the standoffsdisposed therethrough, and a plurality of standoff caps, each comprisinga hollow sleeve disposed on a portion of the securing element protrudingfrom a respective aperture and mechanically restraining the PCB againstthe standoff, wherein the standoff caps are color coded, each coloridentifying a function of the standoff caps.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is an illustration of a system for securing a PCB to a chassisaccording to the prior art.

FIG. 2 is an illustration of a standoff and a connector according to theprior art.

FIG. 3 is an illustration of an exemplary system for securing a PCB to adevice chassis, according to an embodiment of the invention.

FIG. 4A-4B is an illustration of an exemplary standoff and associatedstandoff cap according to an embodiment of the invention.

FIG. 5A-5C is an illustration of an exemplary standoff cap according toan embodiment of the invention.

FIG. 6 is an illustration of an exemplary standoff cap coupled withelectric cables, according to an embodiment of the invention.

FIG. 7 is an illustration of an exemplary standoff cap containing akeying mechanism, according to an embodiment of the invention.

FIG. 8 is an illustration of a system comprising a plurality of colorcoded standoff caps, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide a system for testing andmounting a PCB in a device. A PCB may be placed on one or more standoffsso that a head portion of the standoff protrudes from one or moreapertures of the PCB. A push-pin type standoff cap may then be placed onthe protruding heads to mechanically restrain the PCB to the standoffs.Furthermore, one or more cables may be coupled with the standoff caps toprovide power or test signals to one or more connector pads on the PCB.Therefore, the standoff caps provide a system for aligning, retaining,connecting, terminating, and testing printed circuit boards.

In the following, reference is made to embodiments of the invention.However, it should be understood that the invention is not limited tospecific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice theinvention. Furthermore, in various embodiments the invention providesnumerous advantages over the prior art. However, although embodiments ofthe invention may achieve advantages over other possible solutionsand/or over the prior art, whether or not a particular advantage isachieved by a given embodiment is not limiting of the invention. Thus,the following aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s). Likewise,reference to “the invention” shall not be construed as a generalizationof any inventive subject matter disclosed herein and shall not beconsidered to be an element or limitation of the appended claims exceptwhere explicitly recited in a claim(s).

PCB Alignment and Retention Device

FIG. 3 illustrates improved standoffs 321 according to an embodiment ofthe invention. Standoffs 321 are shown securing PCB 110 to a chassis120. At one end, each standoff 321 may be secured to the device chassis120, or alternatively, to another component, for example, another PCB.As illustrated in FIG. 3, each standoff 321 may include a securingelement 322 (also referred to herein as a “head”) to which a retainingmember can be attached to secure the PCB 110, as will be describedbelow. The heads 322 may be narrower than the remaining body of standoff321. Therefore, the PCB may be placed on the standoff so that the heads322 pass through apertures 112 of PCB 110, as illustrated in FIG. 3. Byproviding heads that easily pass through associated apertures alignmentof the PCB on the chassis can be done quickly and efficiently.

While circular apertures and cylindrical heads are disclosed herein, oneskilled in the art will nevertheless recognize that embodiments of theinvention are not limited by the cylindrical shape of the heads orapertures. Any reasonable shape that allows a head of the standoff toslide through an aperture of a PCB and allowing the PCB to rest on thestandoff may be used. One skilled in the art will also recognize thatany reasonable size of apertures in relation to the heads may beselected to allow the apertures to fit tightly around the head, therebyreducing the lateral movement of the PCB.

The PCB may be secured on the standoffs using standoff caps 330. Thestandoff caps may be made from a suitable insulator material, forexample, polycarbonate material. In one embodiment, standoff caps 330may be “push-pin” shaped and configured to fit snugly around the portionof heads 322 that protrude from apertures 112, thereby providing amechanical restraint to secure the PCB to the standoffs. For example aninner surface of the standoff cap may lock with a head at the interfaceof the inner surface and the head surface, thereby securing the cap tothe head. Thus, standoff caps may be easily installed without the use ofadditional tools or the use of excessive force against the standoffs orthe PCB, thereby minimizing the risk of damage to device components.

FIG. 4A illustrates an exemplary standoff-standoff cap pair in greaterdetail. The standoff may consist of a cylindrical body 402, head 322 anda PCB resting surface 401. The standoff may be made of metal, nylon, orsome other plastic material. A PCB may be placed on surface 401 of astandoff by passing the head through a PCB aperture 112. Standoff cap330 may then be secured to the portion of the head protruding from thePCB to mechanically restrain the PCB.

In one embodiment, head 322 may be threaded to allow the standoff cap tobe tightly coupled with the head. Accordingly, as illustrated in FIG.4B, standoff cap 330 may include a threaded hollow sleeve 403 to screwstandoff cap 330 to head 332. Furthermore, as illustrated in FIG. 4B,the top of head 322 may be dome or conically shaped, which allows headto be easily guided into the sleeve of the standoff cap. Therefore,standoff caps may be easily installed without the use of additionaltools or excessive force. It should be noted that a threaded engagementbetween the outer surface of the head 322 and the inner surface of thehollow sleeve 403 is merely one embodiment. More generally any kind ofinterface providing a degree of resistance to relative axial separationis contemplated. For example, the interface may be defined by respectivefriction surfaces of sufficient roughness.

In some embodiments a gasket 404 may be placed between the standoff cap330 and a PCB as illustrated in FIG. 4B. Gasket 404 may provide a soundconnection between the standoff head and a contact pad on the PCBthrough the gasket. In one embodiment, the gasket may facilitate thegrounding of circuits on the PCB by providing a connection to thechassis through the standoffs. Exemplary gasket materials include rubberand silicone. Conductive gaskets may include impregnated silver in therubber or silicone to facilitate an electrical connection between acontact pad and the standoff head. However, if circuit isolation isdesired, the gasket may be made from a suitable insulator material.

Gasket 404 also fills the space between the PCB and the standoff capwhile under compression. Therefore, gasket 404 may be made from acompressible or slightly compressible material so that it tightly fillsthe space between a standoff cap and PCB, including any irregularitiesin the alignment between the PCB and the standoff cap. Placing a gasketbetween the PCB and the standoff cap may also help absorb shocks to thedevice that may damage the PCB.

In some embodiments, to prevent the standoff cap from being dropped orlost in the device, each standoff cap may be tethered to an associatedstandoff using a lanyard 405 as illustrated in FIG. 4C.

FIGS. 5A-5C illustrate an alternative mechanism to couple standoff cap330 to head 322. As shown in FIG. 5A, standoff cap 330 may include acoupling mechanism 542 within its housing. Coupling mechanism 542 mayinclude a coupling button 562, actuating body 560, a piston 564,compression spring 565, and an inner surface of the standoff cap definedby a plurality of gripping fingers 568. Coupling button 562 may protrudefrom a recess 548 in the housing of standoff cap 330, as illustrated inFIG. 5A. Coupling button may be connected to the piston 564 to movepiston 564 when the coupling button is pressed.

Piston 564 and compression spring 565 may be contained in a cylindricalchamber 548. Compression spring 565 is placed in the cylinder in such amanner that one end of compression spring 565 is adjacent to piston 564and the other end is adjacent to a surface 570 of cylindrical chamber548, as illustrated in FIG. 5A. Compression spring 565 may contain apredetermined amount of tension so that it is biased to push piston 564to the top end 571 of cylindrical chamber 548.

When button 562 is pressed, piston 564 may move away from top end 571,as illustrated in FIG. 5B. Piston 564 may press against compressionspring 565, thereby increasing the tension in compression spring 565.Therefore, when the button is released, spring 565 may push Piston 564back to top end 571.

Piston 564 may be connected to an actuating body 560. Actuating body 560may be configured to move along shaft 588 when the button 562 ispressed. Actuating body 560 may be coupled to a plurality ofcircumferentially arranged gripping fingers 568, as illustrated in FIG.5.

Gripping fingers 568 may be operatively coupled to button 562 andconfigured to move in concert with actuating body 560. When button 562is pressed, gripping fingers 568 may protrude out of opening 569 of thestandoff cap and expand outwards as shown in FIG. 5B. Gripping fingers568 may inherently be biased to flare outwards out of opening 569, intoa receiving configuration, when button 562 is pressed. In this openconfiguration, the fingers define an opening sufficiently large toreceive the head. When the button is released, spring 565 may force thefingers back into opening 569, causing the gripping finger to clasp thehead.

Gripping fingers 568 may contain ridges 580, as illustrated in FIG. 5C.The ridges are provided to engage the gripping fingers to the threadingof a standoff head, thereby locking the standoff cap to the standoffhead. To release a locked in standoff cap, button 562 may be pressed,causing the gripping fingers to move further outwards and away from thethreaded wall of the standoff head, thereby releasing the standoff capfrom the standoff head.

In one embodiment, a member of the cap may press against the head whenthe button is pressed to urge the head axially away from the cap,thereby facilitating the separation of the cap and the head. Forexample, when the button 562 is pressed, actuating body 560 may pressagainst the head, thereby allowing the housing of the standoff to moveaway from the head, thereby facilitating the release of the standoff capfrom the head.

Therefore, the standoff caps can easily be installed or removed makingPCB installation/removal much more efficient and less tedious.Furthermore, because hardly any downward force is required to installcaps with gripping fingers, the risk of damage to the PCB during boardinstallation/removal is also greatly reduced.

PCB Connections and Testing

In one embodiment the standoff 321 may provide an electricallyconductive path between the system chassis and the ground plane orground node on the PCB. A low impedance connection to ground may beessential to the reliability of the PCB. For example, grounding the PCBmay reduce electromagnetic interference. To establish a groundconnection an aperture representing the ground node may be plated withan electrically conductive material. Therefore, when the standoff headis placed in the aperture a connection is established between thestandoff and the ground node.

In some embodiments, in addition to providing support to the PCB,standoff caps may also contain one or more conductive elements which mayprovide temporary or permanent external electric connections between thePCB and and one or more electric cables. For example, standoff cap 330may be coupled with a power cable to provide power to components on thePCB. In other implementations, the standoff cap 330 may be coupled withcables configured to carry test signals, signals from other devices, orto probe the PCB. Securing the standoff cap to a standoff head may causethe cables to connect to one or more connector pads on the PCB throughthe conductive elements, thereby creating a signal path between thecables and the PCB.

FIG. 6 illustrates an exemplary implementation of a standoff cap 330configured to provide external signals to the PCB. As illustrated inFIG. 6, standoff cap 330 may contain one or more through holes 601 inthe flared bottom portion of the cap. Through hole 601 may carry a cable610 as illustrated. Cable 610 may contain a prong 611 that protrudesfrom the bottom of the standoff cap, as shown in FIG. 6. Prong 611 maybe configured to contact a connector pad 620 of the PCB. As illustrated,a plurality of connector pads 620 is provided. The signals carried oncable 610 may be provided to any pad by simply twisting the standoff capso that prong 611 connects to the desired pad.

The above mentioned system for providing external signals to the PCBachieves several advantages over the prior art. For example, prior artrequires a separate connector to be placed on the PCB for each test thatwas to be performed, thereby taking up valuable space on the PCB.Embodiments of the invention obviate the prior art requirement ofplacing multiple connectors by providing multiple connector pads aroundthe same standoff head to conserve space. Different test signals maythen be provided to the PCB by placing a standoff cap with a cablecontaining the desired test signal in such a way that the cable makescontact with the appropriate connector pad.

For example, during a first test, cable 610 may be connected to avoltage source to provide a predetermined voltage to the PCB. Standoffcap 330 may then be connected to the head 322 and twisted so that prong611 connects to a first connector pad. Standoff cap 330 may be removedafter the first test. Subsequently, during a second test, cable 610 maybe connected to a current source to provide a predetermined current tothe PCB. Standoff cap 330 may be connected to the same head 322 andtwisted so that prong 611 connects to a second connector pad. This stepmay be similarly repeated for multiple signals being provided tomultiple connector pads. Therefore, valuable real estate on the PCB maybe saved by avoiding multiple connectors

A further advantage of the standoff caps described in FIG. 6 is that thestandoff caps need not be left on the PCB post testing, thereby makingit reusable. Because standoff caps containing gripping fingers caneasily be installed and removed, the same standoff cap may be used totest multiple boards. This results in significant cost savings over theprior art where potentially gold plated connectors had to be left on thePCB post testing.

In some embodiments, after a standoff cap that is coupled with one ormore test cables and used for PCB testing is removed from a given head,a retaining standoff cap (without cables) may be placed on the head. Theplacement of such a retaining standoff cap may aid in securing the PCBto the standoffs.

While a single cable is shown coupled with the standoff cap in FIG. 6,one skilled in the art will nevertheless realize that multiple cablesmay be coupled with a standoff cap. One or more cables coupled with thestandoff cap may be configured to connect to one or more connector pads,thereby allowing simultaneous imposition of multiple signals and/orparallel testing.

During testing, the standoff cap may twist due to a number of reasons,causing the connection between prong 611 and a particular connector padto be lost. For example, moving a cable coupled to the standoff cap maycause the standoff cap to twist, resulting in a loss of connectionbetween the cable and the PCB. To prevent such undesired twisting, thestandoff cap may be locked in a particular position using a key.

Referring back to FIG. 5C, a slot 553 may be provided in the flaredportion of the standoff cap to lock the standoff cap with a protrusionon the PCB. Slot 553 may wrap around a protrusion on the PCB, therebypreventing twisting of the standoff cap. Alternatively a protrusion maybe provided in the standoff cap that locks the stand off cap by slidinginto a slot on the PCB. FIG. 7 illustrates a standoff cap containingslot 753 and a protrusion 754 for locking the cap. When multipleconnector pads may be accessed by the standoff cap, the particularkeying position may identify the pad, thereby facilitating the couplingof the cable to a particular pad.

In some embodiments, the standoff caps may be color coded to identify afunction of the standoff cap. Exemplary standoff cap functions includePCB retention, testing, and power supply. FIG. 8 illustrates a pluralityof standoff caps coupled to a PCB 110. Standoff caps 801 may be used formechanically restraining the PCB to the standoffs. Accordingly, standoffcaps 801 may all be of the same color, for example, black. Standoff cap802 may be coupled with a power supply supplying power to PCBcomponents. Standoff caps coupled with power supplies may be of a uniquecolor, for example, red. Standoff cap 803 may provide test signals tothe PCB, and may be a separate color, for example blue. Standoff capcolors may also be used to differentiate between different testingfunctions.

Conclusion

The improved standoff system described herein allows faster and moreefficient alignment of PCBs during installation. Furthermore, byutilizing push pin type standoff caps to secure the PCB, the use ofadditional tools and excessive forces to install the PCB is avoided.Therefore, installation of PCBs is accomplished faster and with littleeffort. Moreover, the risk of damage to device components is alsogreatly reduced.

Standoff caps may also be used to provide power and test signals to thePCB by coupling the standoff caps with an electric cable providing thesignals. Each standoff cap may connect to different connector pads onthe PCB to provide an appropriate signal to the pad. Furthermore,because standoff caps are easily removable, they need not be left on theboard, and may be used to test multiple boards. Therefore, the prior artcost of leaving connectors on the PCB is also obviated.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for testing a printed circuit board (PCB), comprising:placing the PCB on a plurality of standoffs, each standoff comprising abody, a securing element disposed in and protruding from the body, and aPCB resting surface formed at an interface of the head and the body,wherein the securing element is narrower than the body thereby allowingeach securing element to register with and be disposed through anaperture formed in the PCB and allowing the PCB to rest on therespective PCB resting surface; securing the PCB to the standoffs byfitting a standoff cap over a portion of each securing elementprotruding from the apertures, wherein one or more of the standoff capsinclude one or more electrically conductive elements coupled to one ormore respective electric cables for carrying test signals; andregistering the one or more conductive elements with one or moreconnector pads on the PCB surface to exchange test sigals with the PCB.2. The method of claim 1, wherein securing the PCB to the standoffcomprises: pressing a coupling button on the standoff cap, wherein thecoupling button, when pressed, causes a plurality of gripping fingers ofthe standoff cap to flare outwardly into a receiving configuration;axially receiving the securing element in an opening defined by theflared fingers; and releasing the coupling button causing the grippingfingers to be biased inwardly into a retaining configuration in whichthe gripping fingers grip the securing member.
 3. The method of claim 2,wherein the securing element is a threaded member.
 4. The method ofclaim 3, wherein each gripping finger comprises ridges configured tolock against the threading of the securing element.
 5. The method ofclaim 2, wherein the plurality of gripping fingers are concentricallyarranged in a hollow sleeve of the standoff cap.
 6. The method of claim2, further comprising removing the standoff cap by pressing the buttonfurther causing the plurality of gripping fingers to flare outwards andaway from the surface of the securing element, thereby releasing thesecuring element.
 7. The method of claim 1, wherein registering the oneor more conductive elements with one or more connector pads on the PCBsurface comprises registering a slot on the standoff cap with aprotruding key formed on the PCB to lock the standoff cap in apredetermined position and prevent the standoff cap from rotating. 8.The method of claim 2, wherein the securing and registering is performedduring a PCB testing phase and further comprising, after the testingphase: removing each standoff cap from the respective securing element;and placing a retaining element on each securing element to secure thePCB to the standoffs.